Such methods and such CT systems are widely known. For instance, vascular diseases are diagnosed in modern medicine on the basis of computed tomography angiography (CTA) slice image data. For better recognition of vascular structures, a contrast agent is injected into the patient's veins when scanning a CTA. After a certain time, the contrast agent reaches the vessels to be imaged via the heart. Since the scan of the patient, during which he or she is moved on a support through the rotating gantry of the computer tomograph, takes a few seconds, the start of the scan must be matched in time to the instant of the contrast agent injection. To this end, in a predetermined slice, slice images are formed at a time interval of about 1 second and the blood vessels recognizable in the section are checked for inflow of contrast agent. If the contrast agent is visible owing to the local change in the image intensities, the scan can be automatically started.
A problem here is that when automating this procedure, before the inflow of contrast agent it is necessary to recognize where a blood vessel lies in the CT image. Since the blood vessels scarcely differ in their absorption from the surrounding organ, the known pattern recognition methods generally do not succeed in this case. In practice, it is therefore usually necessary for a doctor to observe the currently formed CT representations, recognize when an inflow takes place in a blood vessel and correspondingly give the start instruction for the actual CT scan.